RF circuit is a part of RF technology, which is used for transmitting signals at radio frequencies. It is an electronic circuit that can be configured to convert radio frequencies into usable electrical signals and vice versa.
RF circuits are the heart of working with radio on microcontrollers. Basically, they take an input and create an output. It would be impossible to create a signal if you were to remove either the input or the output. When you look into how these circuits work, you will find dozens, if not hundreds, of variations on each circuit. The benefit of these circuits is that they transmit radio signals, which means you can get a signal off your device and to whatever it is you are trying to reach, such as television or thermostat.
Within this article, you will get an introduction to RF PCBs, details on components of RF circuits, their advantages, common materials for RF PCBs, and their design and layout factors.
Table of Contents
Introduction to RF PCB
RF PCB is an acronym for Radio Frequency Printed Circuit Board. RF PCB is a printed circuit board that uses RF technology to transmit and receive data. It comprises copper traces, pads, and other components used to build circuits on the board. It is used to design and build electronic devices. These are mostly used in communication systems, aerospace technologies, high frequency equipment, and military applications. It is important to know that not all circuits are made on RF PCBs. Some circuits use different methods of transmitting information, such as digital and analog signals over radio waves.
In recent years, RF PCB has become increasingly popular in mobile phones and cellular networks. The evolution of RF PCBs started with basic thick copper-clad boards to multi-layered boards that could handle higher frequencies. Nowadays, RF PCBs are made from thin copper layers, making them flexible and lightweight. This makes it possible to integrate them into mobile devices such as laptops, tablets, and smartphones where space is limited, and power consumption is an issue.
The main function of RF PCB is to connect all the different parts of an electronic device while providing isolation between them. The metal traces on the surface can be easily connected to other metal traces or components through solder or other bonding materials. The isolation layer allows for better performance and less noise due to crosstalk between different sections of an electronic device.
Layer Composition of RF PCB
RF PCB comprises two layers; the signal layer and the ground layer. The signal layer is the top layer, consisting of copper traces that provide a path for signals to be transmitted between components and circuits on the board. The ground plane is the bottom layer, providing a return path for current when signals are transmitted.
The layers are laminated together using a high-frequency wave solder fusing process. This process melts the top and bottom layers together, forming an RF connection. The solder fusing process also gives each layer a certain rigidity so that it does not move around to its neighboring materials during use or transport.
The thickness of both layers varies according to the manufacturer’s design requirements, but generally, they are quite thin—between 0.05mm (0.002in) and 0.2mm (0.08in).
RF PCB Materials
RF PCBs are made from materials with excellent electrical properties at high frequencies: copper, gold, or silver plating, and FR4 or Rogers 4350B substrate material. They often also contain ferrites and other materials that can help reduce unwanted noise signals from entering or leaving the circuit board.
There are many different types of materials used in the manufacturing of PCBs. The choice of material will depend on the type of circuit being made, the fabrication process used, and the board’s intended use.
Here is a quick guide to some common RF PCB materials:
- FR-4 – This is the most common material used in RF circuit boards. It offers good mechanical strength and rigidity while still being lightweight. FR-4 is also highly transparent to electromagnetic waves. There are several different grades available with varying levels of electrical and thermal conductivity.
- PTFE – PTFE is a very good dielectric material for printed circuit boards. Very low loss tangent combined with low dielectric constant makes it an excellent choice for high frequency circuits up to 30 GHz or more.
- Polyimide Film – Polyimide film has high dielectric breakdown strength, good thermal resistance, and low moisture absorption rate, making it ideal for use in harsh environments such as aerospace electronics, where reliability is a key issue.
Structures and Components Used in RF Circuits
Some of the structures and components used in RF circuits include:
Antenna
The antenna is an essential part of a radio communications system. It is designed to transmit and receive radio waves. The main function of an antenna is to capture the electromagnetic energy from the transmitter and convert it into electrical energy, which can be transmitted along the transmission line.
Passive and Active Filters
These are used with antennas to select specific frequencies from a larger range of signals. In a passive filter, the filter elements are resistors, capacitors, and inductors that restrict all frequencies except those within the passband. In an active filter, there is an amplifier between each pair of reactive elements (inductors and capacitors). This allows control over both gain and frequency response beyond what can be achieved with passive filters alone.
Resonators
Resonators are used to tune a circuit to the desired frequency. A resonator consists of two or more parallel capacitors or coils connected by resistors or inductors, which allow only certain frequencies to pass through while blocking others.
Amplifiers
Amplifiers are used to increase the amplitude of a signal so it can be transmitted over long distances by increasing its power output. Amplifiers can also be used to increase or decrease the amplitude of a signal without changing its frequency, or to change the frequency without changing its amplitude.
RF Power Splitter, Divider, and Combiner
A power splitter takes a signal and divides it among several outputs. This is useful when sending a signal to multiple receivers. A divider does the opposite — it takes one input and splits it into multiple outputs of lower amplitude. A combiner combines two or more signals into one output signal. It can be used to combine two signals from different sources into one output signal with double the amplitude (gain).
Circulators
A circulator is an electronic device used to steer an RF signal in one direction only through a system of loops and junctions. The circulator allows only one-way energy transmission, isolating it from unwanted back-reflections and feedback. The most common form of the circulator is the quarter-wave coaxial cable transformer.
Waveguide Cavities
In a waveguide cavity, the walls of the cavity act as both reflectors and absorbers for radio waves. The cavities can be designed with different shapes and sizes to create different types of directional antennas.
Attenuators
Attenuators are used in RF circuits to reduce the amplitude of an RF signal. An attenuator can be designed as either an amplifier with a variable gain or a circuit that reduces the signal strength by reducing its voltage or current level. Attenuators are also used to limit the power output from an amplifier, so it does not exceed its rated output power.
RF PCB Benefits
RF PCBs have many benefits:
High Reliability
RF PCBs have been designed for high reliability. They have been tested for many years to ensure they will work correctly under all conditions.
High Performance
RF PCBs can handle large amounts of power and operate at extremely high frequencies (GHz). This makes them ideal for applications such as radar systems and satellite communication networks.
Low Cost
Manufacturing an RF circuit is low compared to other types of electronics because these circuits contain fewer components than other circuit boards. A typical RF circuit may only have a few hundred passive components (capacitors and inductors), whereas an analog IC might have thousands or even more transistors on its surface.
Uniform Distribution of Signal
When you use an RF board, you will find that it provides a uniform distribution of signal across the entire surface area of the board because there are no gaps between traces on the board’s surface like there would be in a standard printed circuit board (PCB). This means there will be no loss of signal strength when using an RF PCB circuit over long distances or through materials with high impedance, such as plastic, rubber, metal sheets, etc.
RF PCB Design and Layout Common Factors
RF PCB design is designing a printed circuit board (PCB) for a radio frequency (RF) system such as a radio, television, or cellular phone,micro via pcb. RF PCB design is similar to digital circuit board (PCB) design in that it involves routing electrical signals through conductive paths on the board. However, RF PCBs are subject to additional considerations due to their operating frequency and the need for shielding to prevent interference with other devices.
The design and layout of an RF PCB are based on many factors, including:
- Transmission frequency range and bandwidth
- Required signal bandwidth
- Interference from other equipment operating at the same frequency range or adjacent frequency ranges
- Duty cycle requirements
- Power consumption requirements
Summing Up
In summary, a PCB or printed circuit board is essential in creating almost any electronic device. With many different applications and a wide range of manufacturing procedures, the possibilities seem endless when it comes to RF PCBs. Now that you know what PCBs are, Hemeixin has written a separate guide on RF and microwave PCBs that might interest you.
